[Ada] Make "gcc -gnatDGL" handle unterminated last lines properly

[Pierre-Marie de Rodat]

This patch fixes a bug in which "gcc -gnatDGL" raises an unhandled
Constraint_Error in checks-on mode if the last line in the file is not
terminated with a line terminator.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sprint.adb (Write_Source_Line): Check for EOF in
	Line_Terminator loop.  Note that when a source file is read in,
	an EOF character is added to the end.
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